Last month, I had several questions about the burn-off system the Silverado HD's diesel uses to get rid of particulates collected by the Diesel Particulate Filter. I wanted to know what physically occurs when burn-off happens, and when the best time is for burn-off to occur, questions that are new ones for anyone who drives one of the DPF diesels from Ford or Chevrolet. And I got some answers from GM, specifically from Gary Arvan, Chief Engineer, Duramax. He explains, "The idle rpm is elevated during "regeneration," which is a term used to describe the warm up, sustained high temperature to oxidize soot, and cooldown of the DPF catalyst. For the LML engine, the idle rpm goes from 640 rpm during non-regeneration to 800 rpm during regeneration. This rpm increase helps sustain temperatures to allow the fastest possible total regeneration cycle. The engine can make a slightly different sound during regeneration as the turbocharger vanes, intake throttle, exhaust gas recirculation, and fuel injection events can all be different during this event." As far as when the best time is for regeneration to take place, he confirmed that "regeneration at higher load is more efficient and initiating regeneration when the DPF is already hot can reduce the warm-up portion of the regeneration cycle and shorten the overall event." So the best time for burn-off to occur is on the open road, as it's less likely to get interrupted and it will take the shortest amount of time. And, in the event that you park your truck before regen is finished-remember, there is no light on the dash to let you know when it's happening-Arvan explained that the regeneration sequence will start over on the next drive cycle. But that only happens if there is still soot that needs to be removed when the engine is shut off.

When I asked him about the driver having some say in prompting the burn-off to happen, he did not sound too positive about it: "Emissions regulations prohibit operator initiated regeneration events. This is done because emissions during a regeneration cycle are different than while not regenerating, and the control system and hardware are designed to regulate the frequency of regeneration and the average engine emissions." I still think this is something that could be controlled by the driver, and I wouldn't be shocked if some aftermarket companies were already looking into this.

I got into this truck after driving a 2011 F-150 for an extended period of time. It was a strong reminder of the difference in ride between a half-ton and a heavy-duty. The Ford's ride was much cushier than in the Silverado 2500HD. As it should be-the Chevy is made to carry a lot more payload and has a much higher towing capacity. But when you get used to the ride on a particular vehicle, it isn't until you have something to contrast it with that you say, "Oh, yeah. This is how different a half-ton feels compared to a three-quarter ton."


Our Vehicle
Months/mi in service 4/3873
Avg econ/CO2 13.8 mpg/1.61 lb/mi
Energy consumption 244 kw-hr/100 mi
Unresolved problems None
Maintenance cost $0
Normal-wear cost $0